The present invention relates to a magnetic recording and reproducing apparatus, and more specifically, to a video tape recorder or audio tape recorder having a rotary drum, hereinafter referred to as a head drum, having at least one and generally two recording heads (referred to in the following as rotary recording heads) fixedly mounted thereon for recording audio or video signals upon a magnetic tape, and in which the head drum further has one or more rotary erase heads (referred to as rotary erase heads in the following, but which are sometimes called "flying erase heads") mounted thereon for erasing recorded signals from the tape.
The rotary recording head records signals in the form of successive signal tracks which are obliquely oriented with respect to the direction of advancement of the magnetic tape, and have a fixed width and pitch. In the prior art, the width of the rotary erase head is made slightly greater than that of the rotary recording head, and erasure is performed by causing the erase head to scan along successive signal tracks. The magnetic tape passes around the head drum to extend around at least 180.degree. of the drum periphery, oriented with respect to the axis of rotation of the drum such as to produce the obliquely directed signal tracks described above as each rotary recording head successively contacts and moves along the tape surface. A recording apparatus employing such helical scanning of the tape will be referred to in the following as a VTR (video tape recorder).
With one type of VTR, rather than utilizing a rotary erase head as described above, a stationary erase head is employed, with the head width being made greater than the width of the magnetic tape. However the rotary erase head provides the advantage that each junction between a previously recorded portion of the tape and a newly recorded portion of the tape will be "clean", i.e. will not generate a temporary disturbance on the display produced by the VTR during subsequent playback of the tape, such as is produced when a stationary erase head is utilized. These disturbances result from the recording head scanning across short portions of the tape, corresponding to the aforementioned junctions, each of which has been erased and which has not been thereafter recorded on.
However a problem which arises with prior art types of magnetic recording and reproducing apparatus employing rotary erase heads is that the degree of erasure of previously recorded material is insufficiently high, using conventional ferrite erase heads. The present applicant has found that this problem can be overcome by employing a rotary erase head of width such that the erase head scans each signal track twice in succession, as described in detail hereinafter. However a problem arises with such an apparatus when data is inserted into a previously recorded portion of the magnetic tape, i.e. is recorded over a part of the previously recorded tape. Specifically, a short portion of signal track which has been erased, and not subsequently recorded on, will remain at the end of each of such inserted recorded portions. These erased portions of the tape result for example in disturbances in the displayed video signal when playback of the tape is performed, in the case of a video tape recorder, and represent a serious problem.